The invention relates generally to protection equipment for electrical circuits, and more particularly to electrical circuit breakers.
A circuit protector device, such as a fuse or circuit breaker, protects an electrical circuit from damage due to over-current and short-circuit conditions. An overcurrent condition occurs when there is too high a level of electrical current flowing in an electrical circuit due to power demand of circuit loads being greater than the design capacity of the electrical circuit. A short-circuit condition occurs when an electrically conductive member makes contact with two points of an electrical circuit causing electrical current to bypass the circuit""s electrical load resulting in extremely high electrical currents. Over-current and short-circuit conditions can damage conductor wires of electrical circuits due to overheating of the conductor wires and result in burning of the wire insulation. Other damage caused by over-current and short-circuit conditions may result with the electrical or electronic equipment found in a particular electrical circuit. In a protected electrical circuit, when an over-current or short-circuit condition occurs, the circuit protector device acts as an open electrical switch thereby preventing additional electrical current from flowing in the protected electrical circuit.
Fuses protect electrical circuits by using a xe2x80x9cfusible linkxe2x80x9d that melts to cause an open circuit condition when the amount of electrical current flowing through the protected electrical circuit exceeds a known level. Circuit breakers use thermal or magnetic based mechanisms that are sensitive to the amount of electrical current flowing through a protected electrical circuit. These thermal and magnetic based mechanisms also cause an open switch condition when electrical current exceeds a known level. Circuit breakers become progressively more expensive, relative to fuses, for applications where the operational level of electrical current is very high. Generally, fuses are less expensive, however, circuit breakers are much more convenient than fuses since they can be reused whereas fuses must be replaced.
Some challenging applications of circuit breakers involve environments having at least one of the following conditions: high temperature, high humidity, and inherent vibrational forces. The marine environment has these characteristics. Circuit breakers generally have many components that increase the cost of their manufacture. Further, these many components must perform reliably both as individual components and as a collective unit. Given the convenience of circuit breakers compared to fuses, there is much motivation for improving circuit breakers to further extend their scope of application and reduce their cost of manufacture while maintaining and increasing their reliability and performance characteristics.
The present invention resides in a method and system for an advanced circuit breaker including a housing, first and second electrical terminals, a contact arm, a cam up, a torque generating member, and a bimetal blade. The first and second electrical terminals are affixed to the housing and are configured to electrically couple the electrical circuit breaker to the electrical circuit. The contact arm includes first and second portions.
The first portion of the contact arm is electrically coupled to the first terminal and some aspects included being rotatably mounted within the housing. The second portion of the contact arm has an arm contact affixed and electrically coupled thereto.
Some aspects included the cam having first and second portions wherein the first portion is rotatably mounted within the housing. In some aspects, the second portion is movably coupled to the contact arm such that rotation of the cam in a first rotational direction through a first amount of rotation causes rotation of the contact arm in a second rotational direction and further rotation of the cam in the first rotational direction through a second amount of rotation beyond the first amount of rotation causes rotation of the contact arm in a direction counter to the second rotational direction. In some aspects, the torque generating member is configured to apply a torque to the cam tending to rotate the cam in the first rotational direction.
In some aspects, the bimetal blade is electrical coupled to the second electrical terminal and is configured to change shape based upon an amount of electrical current above a threshold level passing through the bimetal blade for at least a predetermined amount of time. The bimetal blade has a blade contact affixed and electrically coupled thereto. The bimetal blade is shaped and positioned with respect to the contact arm such that the blade contact contacts the arm contact to prevent the contact arm from rotating in the second rotational direction when the amount of electrical current flowing through the bimetal blade is below the threshold level. Further aspects included the bimetal blade being shaped and positioned with respect to the contact arm to allow the contact arm to rotate in the second rotational direction with the cam rotating in the first rotational direction through the first amount of rotation and to allow the contact arm to remain in contact with the blade contact when the amount of electrical current flowing through the bimetal blade increasingly exceeds the threshold level by up to a first amount of electrical current for at least at predetermined amount of time.
Other aspects include the electrical circuit breaker further comprising a conductive shaft electrically coupled to the first terminal and wherein the first portion of the contact arm is electrically coupled to the first terminal through the conductive shaft. Alternative aspects include the electrical circuit breaker having a camshaft rotatably mounted within the housing and wherein the cam is fixedly attached to the camshaft.
Other aspects include the bimetal blade being further shaped and positioned with respect to the contact arm such that when the amount of electrical current flowing through the bimetal blade exceeds the first amount, the blade changes shape and position with respect to the contact arm to cause the blade contact to stop contacting the arm contact and thereby allow the contact arm to rotate counter to the second rotational direction with the cam rotating in the first rotational direction through the second amount of rotation beyond the first amount of rotation.
Other aspects include the electrical circuit breaker further comprising a breaker throw lever fixedly attached to the cam such that a torque applied to the breaker throw lever opposite and exceeding the torque applied to the cam will prevent the contact arm from rotating when the bimetal blade changes shape and position with respect to the contact arm as the electrical current through the bimetal blade exceeds the threshold level for at least a predetermined amount of time. Further aspects include the contact arm having first and second contact arm rails extending longitudinally away from the first portion of the contact arm and substantially parallel to one another. Each of the first and second contact arm rails having a contact arm slot extending longitudinally within and having a cam slidably retained thereto to movably connect the cam to the contact arm.
Other aspects include the cam having first and second cam arms extending longitudinally away from the first portion of the cam and substantially parallel to one another. The first and second cam arms have a pin coupled thereto and extending therebetween and a roller so mounted on the pin to rollably engage the contact arm.
Other aspects include the bimetal blade configured and positioned to change shape and position with respect to the contact arm based upon the amount of electrical current passing through the bimetal blade above the threshold level and independent from rotational position of the cam. Further aspects include the bimetal blade being a snap disc or having the shape of a Valverde blade. Further aspects include the contact arm being sized and positioned with respect to the bimetal blade such that the arm contact maintains substantial contact with a blade contact without electrical arcing occurring between the arm contact and the blade contact as the bimetal blade changes shape and position with respect to the contact arm and as the cam rotates through the first amount of rotation.
Other aspects include the electrical circuit breaker having a conductive shaft electrically coupled to the first terminal and wherein the first portion of the contact arm is electrically and rotatably coupled to the conductive shaft. Further aspects include the electrical circuit breaker having an electrically conductive bearing lubricated with electrically conductive lubricant and configured to electrically and rotatably couple the first portion of the contact arm to the conductive shaft. Other aspects include the torque generating member being a spring shaped and positioned to apply a torque to the cam in the first rotational direction. Other aspects include the electrical circuit breaker having a camshaft having the cam rotatably mounted thereto and wherein the spring is coupled to the cam. Other aspects include a camshaft being coupled to the housing and wherein the cam is rotatably mounted on the camshaft.
Other aspects include the breaker throw lever being fixedly attached to the camshaft such that the position of the breaker throw lever indicates whether the arm contact and the blade contact are in contact with one another. Other aspects include the housing having a housing cover which includes an opening with the camshaft projecting therethrough and beyond an exterior surface of the housing cover and configured for attachment of the breaker throw lever thereto and also having a seal positioned with respect to the camshaft, the breaker throw lever, and the opening of the housing cover to prevent fluids from entering into an internal containment area of the housing from areas adjacent to the external surface of the housing cover.
Other aspects include a current sensitive structure electrically coupled to the second electrical terminal configured to change shape based upon amount of electrical current above the threshold level passing through the current sensitive structure for at least a predetermined amount of time. Other aspects include a linkage coupled to the contact arm configured to apply rotational torque to the contact arm tending to rotate the contact arm in a rotational direction from the first position with contact arm to the second position the contact arm.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.